Concepts of kubernetes components

Preface

Kubernetes There are too many concepts in , what PodServiceDeployment Etc., etc. , I was blindfolded by the people I just touched . Through a few days of observation , Tell me about my understanding of each component .

This article only gives a brief introduction to these concepts , Not to be confused when reading other articles later .

Node

Node Well understood. . Is an instance of the actual operation of the service , It could be a physical machine , It can also be a VM virtual machine

Pod

docker All used , That's the container. . and Pod In fact, it's similar to docker-composer, Multiple associated containers form a Pod. Let's say I have a nginx Container and a php-fpm The container of , The two of them can be combined into one Pod`.

In the same Pod in , Different containers share network stacks and storage volumes . in other words , nginx visit php-fpm You can use it directly localhost:9000 that will do , in other words , One Pod Start two containers in , All occupied 80 port , Can't start successfully . Sharing is through Pause Containers Realized , Here is a brief introduction to the concept , It doesn't unfold .

Pod controller

stay Kubernetes in , Pod It is the smallest unit of resources . And this pile of controllers , It's used to deal with Pod For automatic management . Of course , If you do not use the controller but manage it manually, it is not impossible , Just tired . such as :

• management Pod The number of
• Realization Pod Elastic expansion of
• monitor Pod The state of
• Start and release regularly Pod
• wait

In order to meet different needs , There is a difference Pod controller . The following controllers only implement different requirements , It's just a matter of time .

ReplicationController

Yes Pod Quantity management . Make sure Pod Keep the quantity at the user-defined quantity . ( If the container exits abnormally , Automatically create new Pod. If the number is large , It will also be recycled automatically . ) But now it is recommended to use ReplicaSet Replaced the .

ReplicaSet

and ReplicationController It's about the same , An additional set selector Support for ( tag chooser ).

although ReplicaSet Can be used alone , But recommended Deployment Conduct management .

Deployment

Deployment Will not directly manage Pod, It's through management ReplicaSet, Re Jingyou ReplicaSet management Pod.

Deployment Handled a lot ReplicaSet Unsupported additional actions . Such as :

• rolling-update ( Scroll to update ) And rollback
• Automatic telescopic ( Expand and shrink )
• Pause and resume
• wait

By the way , Deployment Hot update of , By creating a new ReplicaSet, Gradually reduce the original ReplicaSet in Pod Number and add new ReplicaSet in Pod Quantity to achieve . Rollback is the reverse .

HorizontalPodAutoscaler

HPA Will not directly manage Pod, It's management Deployment perhaps ReplicaSet.

HPA It can detect Pod Resource utilization , Such a scenario can be realized : When Pod CPU The utilization rate is greater than 80 Automatically create a new , Otherwise, it will be released automatically . Started at the same time Pod The largest number 30 individual , least 5 individual . It can realize the horizontal expansion of services .

StatefulSet

StatefulSet To solve the problem of stateful service . The above controllers are stateless . StatefulSet The following functions can be realized :

• Stable persistent storage . When Pod After dynamic adjustment, the same persistent data can be accessed . be based on PVC Realization
• Stable network identity . Pod After dynamic adjustment PodNameHostName unchanged . be based on Headless Service Realization .
• Orderly deployment . Previous Pod Successful launch , To create the next Pod. Solve the problem of service dependency . be based on init containers Realization .
• In order to delete . Reverse operation of orderly deployment .

DeamonSet

Can ensure that all ( Or a designated part of )Node All run one Pod copy . When new Node When you join a cluster, you will automatically add the corresponding Pod, When Node When removing from a cluster , Corresponding Pod It will also be recycled .

This runs in Node Medium Pod What's the use ? For example, resource monitoring , Another example is log collection .

Job

Batch task . kubernetes One or more of this task can be guaranteed Pod A successful ending , If the task fails , kubernetes It will restart automatically , Until success .

CronJob

Job Of crontab edition . Based on time management Job. By creating... At a specific time Job Realized . You can run a task at a specified time , Or run periodically at a specified time .

Service discovery and load balancing

Service

Pod The controller is just for Pod Management of , Like in one Deployment Running on 5 individual Pod, If external access Pod The service is written for every Pod The address of , When Pod When scaling dynamically , Maintaining these addresses is a big problem .

and Service It is to solve this problem that . It's a group of Pod It provides a unified external interface , External access Service Re Jingyou Service Send the request to Pod, Without concern Pod The number of 、 start-up 、 Release and so on .

meanwhile Service It can also load balance the traffic

Ingress

because Service Four layer load balancing , In other words, it can only be represented to IP layer , Can't achieve something like nginx Load balancing according to different domain names and different paths . In order to solve this problem Ingress, Ingress It forwards requests independently of other services . It can be understood as Service Of Service.

Generally speaking , adopt Service Yes Pod Internal agency , And then through Ingress Forward the request to Service. Ingress There are also different implementations , And one of the more commonly used is ingress-nginx 了 , Its configuration file is similar to nginx. Officially maintained . The start command is :

kubectl apply -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/controller-v1.1.0/deploy/static/provider/cloud/deploy.yaml

Official documents : https://kubernetes.github.io/ingress-nginx/

Storage volume

This demand is very common , Used to store and mount data . In different containers 、 And different pod To share .

The specific usage can be seen : https://hujingnb.com/archives/709

ConfigMap

Dedicated to storing configuration files , It also supports binary content . Write the contents of the file directly to yaml Configuration in progress . meanwhile , ConfigMap It supports hot update .

Secret

Store some information that needs to be encrypted , Like keys 、 Password etc. . It is basically the same as ConfigMap almost , The difference is ConfigMap The content is encrypted on the basis of . But, uh , At this stage Secret The encryption method of is base64? This is also called encryption ? It can only be counted as coding .

By command : kubectl get secrets secret-name -o yaml View content .

however , The community should introduce more secure encryption policies in the future .

in addition , For private image repositories , Secret You can add authentication information when you pull an image .

volume

In the same pod Storage volumes are shared among multiple containers under , It's like mounting a disk . volume No separate kind, Is defined directly .

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Above , Yes Kubernetes The names in are briefly introduced , Go back to other articles , Is it much clearer . It's all about managing all aspects and levels of the container .

Link to the original text : https://hujingnb.com/archives/706